Designing with diversity on sockets

[Bobby34]

Could somebody put into lamens terms for me what the diversity is on final circuits (sockets) as per table A2 in the OSG.

It reads:
"100% of current demand of largest circuit +40% of current demand of every other circuit".

Does "largest circuit" mean longest length, most sockets, or biggest demand?

Would you then work out what load would be on the largest circuit and add that to 40% of the total load on the other circuits?

Finally would that effectively mean you would apply the same load when calculating cable size to each final circuit?

I think i've i've over read this and confused myself DOH!

In simple terms i'm working through the design process for a simple 2 bedroom house, a ring final upstairs, a radial downstairs and a ring final for the kitchen + radials for oven/hob etc it's just the sockets i'm getting confused with what diversity to apply.

Many thanks in advance

 

[buzzlightyear]

http://www.napitonline.com/downloads/CP 4 07 P 10-11 16th Diversity.pdf I HOPE THIS WILL HELP .

 

[Loki]

say you have multiple rings on a 32A mcb type b


Then 100% (32A) for that ring
Other ring would be at 40% (32 × 0.4 = 12.8A)

32 +12.8 + 12.8 ect

 

[Strima]

That OSG max demand/diversity calculator is a little out of date, all well and good when granny had a couple of three bar heaters chugging away and a few 60 watt incandescent lamps heating the planet up.

Think about what actually runs domestically from a socket circuit.

In bedrooms there's the odd alarm clock, bedside lamp, TV, phone charger, toothbrush charger, shaver socket, occasionally the odd hair dryer and curling tongs etc. So realistically no more than say five amps.

In living areas you have the usual TV, DVD player, possibly computer, internet router, standard lamps, phone chargers etc. Again not a massive amount say around another five amps.

The odd time you may get the vacuum cleaner running around.

Kitchen is where you have your bigger appliances with larger current draw. So kettle, washing machine, dishwasher and tumble dryer. I've left an oven and cooker out of this for now as they would normally be on their own circuits. The appliances rarely run at the same time so potentially your could base your calculation on your highest rated device and add 50% for good measure. Say around 15 amps.

So there you have a basic domestic property drawing around 25 amps at a guess, TBH they're normally a lot lower than that.

This doesn't take into account electric showers, heating, instantaneous water heaters etc.

Maximum demand is really a 30 minute snap shot at one moment in time. You will get the odd spike when the tumble dryer and kettle are running at the same time then Doris decides to do the ironing whilst Desmond is hoovering upstairs, but how often does that happen?

By looking at maximum demand you can then start to work out your diversity and how to balance your circuits for maximum effect.

And then use a bit of SWAG, scientific wild arsed guess...

TBH general use sockets in a two bed domestic property you could get away with a couple of 20 amp radials with a 32 amp RFC for the kitchen/utility room.

 

[Bobby34]

http://www.napitonline.com/downloads/CP 4 07 P 10-11 16th Diversity.pdf I HOPE THIS WILL HELP .

Thanks buzzlightyear so this is more applicable to the maximum demand for the mainswitch and fuse rather than the cable selection. So in regards to cable selection I can still use common sense in regards to thinking of what will be used on said circuits and then checking cable size and mcb against that?

 

[buzzlightyear]

how to apply diversity to a circuit - Bing video - https://www.bing.com/videos/search?q=how+to+apply+diversity+to+a+circuit&docid=608044016193110053&mid=AE962868D8EC7F9F2690AE962868D8EC7F9F2690&view=detail&FORM=VIREHT

 

[Harry_P]

say you have multiple rings on a 32A mcb type b


Then 100% (32A) for that ring
Other ring would be at 40% (32 × 0.4 = 12.8A)

32 +12.8 + 12.8 ect

I don't think that is how to apply diversity. As far as I know you should assess the expected loading of the circuits and then apply diversity . I know it's a misunderstood process but you definitely don't just subtract 60% of the mcb rating.

 

[Bobby34]

It seems to be a little confusing as you can apply diversity when it comes to individual circuits i.e a cooker circuit but then there is also the diversity you would apply to work out the Maximum demand of the whole installation (what you enter on the installation certificate).

Most the circuits are easy to calculate and you can either use actual loads if you know them or can use the book methods but its the socket circuits because if I calculated it the way the book states my socket circuits have the potential demand of 64amps which bumps up my maximum demand to 100amps when my fuse is rated at 80.... thats just not realistic or close to being realistic unless a heater was plugged into every socket.

 

[buzzlightyear]

It seems to be a little confusing as you can apply diversity when it comes to individual circuits i.e a cooker circuit but then there is also the diversity you would apply to work out the Maximum demand of the whole installation (what you enter on the installation certificate).

Most the circuits are easy to calculate and you can either use actual loads if you know them or can use the book methods but its the socket circuits because if I calculated it the way the book states my socket circuits have the potential demand of 64amps which bumps up my maximum demand to 100amps when my fuse is rated at 80.... thats just not realistic or close to being realistic unless a heater was plugged into every socket.

I use the rule of thumb, just bang it in .

 

[Harry_P]

It seems to be a little confusing as you can apply diversity when it comes to individual circuits i.e a cooker circuit but then there is also the diversity you would apply to work out the Maximum demand of the whole installation (what you enter on the installation certificate).

Most the circuits are easy to calculate and you can either use actual loads if you know them or can use the book methods but its the socket circuits because if I calculated it the way the book states my socket circuits have the potential demand of 64amps which bumps up my maximum demand to 100amps when my fuse is rated at 80.... thats just not realistic or close to being realistic unless a heater was plugged into every socket.

That is why you don't try to calculate it that way,If you calculate it that way then you will find many consumer unit's that are protected by a 100 amp main switch but the demand after the incorrect diversity calculation is still more than 100 amps

 

[Bobby34]

I use the rule of thumb, just bang it in .

Hahaha think il be following suit

 

[Bobby34]

That is why you don't try to calculate it that way,If you calculate it that way then you will find many consumer unit's that are protected by a 100 amp main switch but the demand after the incorrect diversity calculation is still more than 100 amps

Yes this is what I am finding, how do you calculate the maximum demand for the socket circuits?

 

[Harry_P]

Yes this is what I am finding, how do you calculate the maximum demand for the socket circuits?

You assess the expected load and apply diversity to that figure,for example if you have 2 socket circuits then 100% of the first circuit is 32 amps and you then assess the second circuit and what is the expected loading if the second circuit?
There is a good video by John ward on YouTube that may help you because he does the sums and explains it very straight forward and simple.
Search diversity John ward on YouTube

 

[buzzlightyear]

You assess the expected load and apply diversity to that figure,for example if you have 2 socket circuits then 100% of the first circuit is 32 amps and you then assess the second circuit and what is the expected loading if the second circuit?
There is a good video by John ward on YouTube that may help you because he does the sums and explains it very straight forward and simple.
Search diversity John ward on YouTube

post 6#done keep up at the back .

 

[Pete999]

Could somebody put into lamens terms for me what the diversity is on final circuits (sockets) as per table A2 in the OSG.

It reads:
"100% of current demand of largest circuit +40% of current demand of every other circuit".

Does "largest circuit" mean longest length, most sockets, or biggest demand?

Would you then work out what load would be on the largest circuit and add that to 40% of the total load on the other circuits?

Finally would that effectively mean you would apply the same load when calculating cable size to each final circuit?

I think i've i've over read this and confused myself DOH!

In simple terms i'm working through the design process for a simple 2 bedroom house, a ring final upstairs, a radial downstairs and a ring final for the kitchen + radials for oven/hob etc it's just the sockets i'm getting confused with what diversity to apply.

Many thanks in advance

Ashley Banjo will know all about "Diversity"

 

[Pete999]

Ashley Banjo will know all about "Diversity"

You OK Buzz?

 

[telectrix]

i know his brother..... SWA Banjo

 

[Loki]

I don't think that is how to apply diversity. As far as I know you should assess the expected loading of the circuits and then apply diversity . I know it's a misunderstood process but you definitely don't just subtract 60% of the mcb rating.

I never said to just subtract 60% the figures are in the onsite guide, i just used what the OP had posted ie 40%.

Ive recently passed the design section on my apprenticeship & we we're tought that unless you can guarantee ie know for certain what is going to be plugged into the ring or radial then you go by the protective device rating & then apply diversity

 

[Loki]

I don't think that is how to apply diversity. As far as I know you should assess the expected loading of the circuits and then apply diversity . I know it's a misunderstood process but you definitely don't just subtract 60% of the mcb rating.

I never said to just subtract 60% the figures are in the onsite guide, i just used what the OP had posted ie 40%.

Ive recently passed the design section on my apprenticeship & we we're tought that unless you can guarantee ie know for certain what is going to be plugged into the ring or radial then you go by the protective device rating & then apply diversity

 

[Bobby34]

I never said to just subtract 60% the figures are in the onsite guide, i just used what the OP had posted ie 40%.

Ive recently passed the design section on my apprenticeship & we we're tought that unless you can guarantee ie know for certain what is going to be plugged into the ring or radial then you go by the protective device rating & then apply diversity

I applied the OSG method to the 2 ring finals and 1 radial (32 + 40% of 32+16) and then applied 100w per light fitting to the lights and did the loads for the actual boiler and oven (plus 5a for socket) and it all comes in at 77a so just less than the 80a fuse so i will put that on the certificate even though 51 amps for the socket circuits is crazy haha.

Thanks for the help people not been on the forum for long but its proving really useful